This invention relates generally to equipment for resurfacing highways and streets, and more particularly concerns equipment for providing, in a single pass, resurfaced roadway which will stand up to traffic wear and tear for a long time.
Macadam highways and streets have been built extensively in recent years. In general, these highways are laid over a base which can include a gravel or similar substructure, and in some instances they include an upper course of concrete. In its upper strata, the highway includes a macadam top surface formed of stone or gravel aggregate bound firmly together by a bituminous bonding agent such as asphalt. This asphalt bonding agent comprises a number of petroleum chemicals which have various melting, pour, and evaporative characteristics.
Such roads provide a relatively trouble-free permanent surface. Inevitably, however, the passage of time and traffic and the impingement of weather causes the macadam surface to become brittle and crack. Where concentrated cracking occurs, pieces of pavement may become dislodged. This dislodgement can create traffic hazards, and it accelerates the deterioration of adjacent pavement and highway substructure. Even if cracking and the loss of pavement pieces do not occur, the passage of traffic can polish the upper highway surface, and a polished, slippery highway surface may be dangerous. In addition, traffic-caused wear can groove or trough a highway surface. Under wet highway conditions, water can collect in these troughs and set up dangerous vehicle hydroplaning phenomena.
The repair of macadam roadways has thus become an important activity in recent years. To motorists, this repair work is essential for easy, care-free driving. To governmental departments and others in charge of street and highway repair, this activity can constitute a major portion of a budget. To repair contractors, such work can be profitable if it is done rapidly, effectively, and at low cost. But repairing these deteriorated highways and streets can be an expensive and difficult task if the repair contractor believes it necessary to remove macadam material, transport that material to a centralized, stationary, recycling plant, and bring new and recycled material back to the road site.
Use of such stationary macadam plants can be avoided, however. Equipment for repairing and resurfacing macadam highways and streets in situ has met with considerable commercial success. Equipment of this sort is described and claimed, for example, in Cutler U.S. Pat. Nos. 3,361,042; 3,724,445; 3,807,886; 3,874,366; 4,008,975; 4,011,023; and 4,124,325. In general, this equipment takes the form of a mobile chassis which carries various heating, scarfiying, mixing, and material handling systems. An engine, a fuel system and electrical and hydraulic devices operate these main systems. The machine or vehicle can be on the order of fifteen feet wide and sixty feet long; it is intended to move along a roadway with some dozen attendant workers at a rate of speed on the order of ten to thirty-five feet per minute. As the machine operates, the old road surface is excavated and combined with additional material, both solid and liquid, to form a new road surface during a single continuous machine pass. During the single continuous pass, the old road surface in front of the machine is excavated and converted into a refinished, smooth, new road surface at the rear of the machine. Solid materials are added to excavated and mixed recycled material to compensate for solids which have been lost as a result of pot holes in the road. Liquid material is added to replace asphalt binder material which has evaporated or which has been lost through water washing or other action.
Observations of macadam pavement, both new and recycled, indicates that extra structural strength and advantage can be obtained when two pavement lifts are provided. The first lift constitutes recycled material laid over an existing substructure or hot mix pavement surface, and a second lift, constituting entirely new hot mix, is laid over the first, recycled lift. Apparently the lower first lift acts as a relatively soft layer that relieves stresses otherwise applied to the new top surface layer. By providing these two layers, the rate at which existing cracks in the old subsurface reflect through pavement is much reduced.
It is accordingly the general object of the present invention to offer repaving equipment which will provide two pavement lifts in a single pass. More specifically, it is an object of the present invention to provide repaving equipment which will provide a bottom lift of recycled, rejuvenated material over existing roadway substructure, and a top lift of entirely new material.
It is another object of the invention to provide recycling equipment which will accommodate variations in necessary thickness of the lifts at one side of the repaving machine operation independently of the thickness requirements found at the other side of the repaving operation.
Yet another object is to offer repaving equipment having sensors and automatic controls for adjusting the amount of repaving material delivered to the road site.
Still another object is to provide a repaving machine which can be disassembled for easier shipment to distant job sites, and which can be easily and quickly assembled into a ready-to-operate repaving machine.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings. Throughout the drawings, like reference numerals refer to like parts.